Photolithography is commonly used in the production of microelectronic circuits and boards. Typical photolithography systems use a mask to impose a pattern using ultraviolet (UV) light. The patterned UV light then impinges onto a substrate or board that has been coated with a UV light sensitive photoresist. The photoresist that is exposed to the UV light undergoes a chemical change that either allows it to be removed with a chemical (but does not affect the unexposed photoresist) or protects it from a chemical that removes the unexposed photoresist. In any event, photolithography allows the pattern on the mask to be reproduced onto the substrate. The patterned substrate is then processed to produce a microelectronic circuit.
FIG. 1 depicts a typical photolithography system 10. The system 10 includes a UV light source 11. UV light from the light source 11 is provided to the mask 13 by the optics of the illumination system 12. UV light, with the pattern of the mask 13, is guided to the substrate 15 by the optics of the projection system 14. In some systems, the entire mask is illuminated at the same time. In other systems, only a portion of the mask is illuminated at a time. In these systems, one or more of the illumination system 12, projection system 14, and platform 16 that supports the substrate 15 and/or mask 13, may be moved to illuminate different areas of the mask 13.
There are several problems with this arrangement. One problem is that many masks are needed to produce the simplest of microelectronic circuits. Complex circuits, e.g. processors, may require many more. Thus, each time a different layer is going to be formed, a different mask needs to be used. Thus, the masks must be loaded and unloaded from the lithography machines. Each mask must be carefully handled, stored, and inspected. Any contamination or damage will result in a faulty product. Another problem is that once the masks are created, they cannot be changed. Thus, simple design changes, even a change in scale, will require the creation of a new set of masks.
Prior attempts to solve these problems has been to us a spatial light modulator (SLM) instead of the mask. The image formed by the SLM is dynamic and thus, one SLM can replace all of the masks. The SLM can be readily changed to reflect changes in designs. This additionally removes the problems associated with handling, storing, and inspecting of the masks. One type of SLM is a liquid crystal SLM. However, current art liquid crystal SLM cannot be used in photolithography systems since the ultraviolet light causes the liquid crystal material to decompose, and the SLM to fail.